International Survey of Herbicide-Resistant Weeds

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(Lactuca serriola)

Auxin Mimics HRAC Group 4 (Legacy O)

United States, Washington
Prickly Lettuce (Lactuca serriola) is a dicot weed in the Asteraceae family.  In Washington this weed first evolved resistance to Group 4 (Legacy O) herbicides in 2007 and infests Cereals.   Group 4 (Legacy O) herbicides are known as Auxin Mimics (Auxin Mimics ).  Research has shown that these particular biotypes are resistant to 2,4-D, dicamba, and MCPA and they may be cross-resistant to other Group 4 (Legacy O) herbicides.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

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QUIK STATS (last updated Jan 31, 2008 )

Common NamePrickly Lettuce
SpeciesLactuca serriola
GroupAuxin Mimics HRAC Group 4 (Legacy O)
Herbicides2,4-D, dicamba, and MCPA
LocationUnited States, Washington
Contributors - (Alphabetically)Ian Burke 
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2,4-D resistant prickly lettuce (Lactuca serriola L.) in Washington. I. C. Burke*,1 J. Yenish,1 D. Pittmann,1 R. Gallagher2; 1Washington State University, Pullman, WA, 2Pennsylvania State University, University Park, PA

Prickly lettuce has become a widespread and troublesome weed in the Pacific Northwest. It occurs in all rainfall zones and is difficult to control largely due to ALS resistance but also due to increased tolerance to 2,4-D and glyphosate. Although prickly lettuce is not a relatively competitive weed in-crop, it can deplete the soil of moisture for following crops. In wheat fields adjacent to Pullman, WA, several individual plants within a prickly lettuce population were observed to survive two separate broadcast applications of a glyphosate plus 2,4-D in mixture (0.84 kg ae/ha each). Other broadleaf weed species and most prickly lettuce plants within the treated area were effectively controlled. Consequently, seed were collected from the surviving plants to determine tolerance to glyphosate and 2,4-D. The objectives of this study where to identify any antagonistic interactions of 2,4-D and glyphosate for control of prickly lettuce and to determine response of putatively resistant prickly lettuce biotypes to increasing rates of 2,4-D. When glyphosate and 2,4-D where applied in mixture at 0.42 kg ae/ha, antagonism was observed in prickly lettuce found to be resistant to 2,4-D. Conversely, synergism was observed when the same treatment was applied to susceptible prickly lettuce. In dose response experiments, the resistant prickly lettuce biotype was found to be 27-fold more resistant to 2,4-D than the susceptible biotype. The resistant prickly lettuce biotype is cross-resistant to MCPA and dicamba, but not to aminopyralid or fluroxypr.

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Confirmation Tests

Field, and Greenhouse trials comparing a known susceptible Prickly Lettuce biotype with this Prickly Lettuce biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetic studies on HRAC Group 4 resistant Prickly Lettuce have not been reported to the site.  There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature
Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database.  If you know anything about the mechanism of resistance for this biotype then please update the database.
Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes.  If you have any information pertaining to the fitness of Group 4 (Legacy O) resistant Prickly Lettuce from Washington please update the database.
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Associate Professor - Weed Scientist
Washington State University
Department of Crop And Soil Sciences
163 Johnson Hall PO Box 646420
Pullman, 99164, Washington
United States
Email Ian Burke
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Washington have been instrumental in providing you this information. Particular thanks is given to Ian Burke for providing detailed information.
Herbicide Resistant Prickly Lettuce Globally
(Lactuca serriola)
Herbicide Resistant Prickly Lettuce Globally
(Lactuca serriola)
Drag a column header and drop it here to group by that column
Herbicide Resistant Prickly Lettuce Globally
(Lactuca serriola)
#CountryFirstYearSituationActive IngredientsSite of Action
1 Australia (South Australia) AustraliaSouth Australia1994 Canola, Roadsides, Spring Barley, and Wheat chlorsulfuron, flumetsulam, metosulam, metsulfuron-methyl, and triasulfuron 1 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
102Lactuca serriolaPrickly Lettuce26
2 Australia (Victoria) AustraliaVictoria2009 Spring Barley, and Wheat chlorsulfuron, and metsulfuron-methyl 1 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
102Lactuca serriolaPrickly Lettuce5516
3 Australia (Victoria) AustraliaVictoria2015 Fallow glyphosate 1 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)
102Lactuca serriolaPrickly Lettuce11022
4 United States (Idaho) United StatesIdaho1987 Canola, Cereals, Chickpea, Lentils, Peas, and Wheat chlorsulfuron, imazethapyr, metsulfuron-methyl, thifensulfuron-methyl, triasulfuron, and tribenuron-methyl 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
102Lactuca serriolaPrickly Lettuce230
5 United States (Washington) United StatesWashington1993 Cereals, and Wheat chlorsulfuron 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
102Lactuca serriolaPrickly Lettuce518
6 United States (Oregon) United StatesOregon1993 Wheat chlorsulfuron, metsulfuron-methyl, and triasulfuron 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
102Lactuca serriolaPrickly Lettuce1174
7 United States (Washington) United StatesWashington2007 Cereals 2,4-D, dicamba, and MCPA 45 Auxin Mimics ( HRAC Group 4 (Legacy O)
102Lactuca serriolaPrickly Lettuce5328
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